The present invention relates generally to bonding pad formation used in integrated circuits, and specifically to a method of attaching a Cu wire to a Cu bonding pad.
Copper (Cu) is gradually replacing aluminum (Al) as the interconnect material in integrated circuits. However, a problem arises due to the fact that the top layer Cu pad does not form a good connection with the normal bonding techniques. This is mainly due to the poor quality of copper oxide formed on the Cu pad surface upon exposure to the atmosphere and moisture.
In order to ensure a good contact between the chip and the bonding element, either the top Cu metal layer has to be replaced by Al, or an indirect way of bonding is needed. Both of these options increase the complexity and cost.
U.S. Pat. No. 5,989,993 to Zakel et al. describes a method for the preparation of bumps for the bonding of integrated circuits using two subsequent metal depositions. The first metal deposition is thicker than the second deposition.
The second deposition is more even throughout a large area than is the first deposition.
U.S. Pat. No. 5,909,633 to Haji et al. describes a method of manufacturing an electronic component by forming copper pads as electrodes on a surface of a substrate; forming a nickel barrier metal layer over the copper pads; forming a gold layer over the nickel barrier metal layer by plating. A semiconductor element is mounted on the substrate by fixing by heating with a thermosetting adhesive. Any nickel compound formed on the surface of the gold layer is removed by heating by plasma etching. Resin is molded to seal the semiconductor element on the surface of the substrate and a solder portion is formed on the gold layer not sealed with the resin.
U.S. Pat. No. 5,715,989 to Kee describes a low temperature method of securing a wire to a bond pad in a semiconductor device. A friction weld is achieved by rotating either the bond pad or wire while in contact until the interface of the wire and bond pad diffuse into each other sufficiently to provide a bond therebetween upon cooling. The method permits the welding of dissimilar metals as well as metals such as copper wire and copper bond pad, copper wire and aluminum bond pad, and wire copper and titanium tungsten bond pad.
U.S. Pat. No. 5,940,680 to Lee et al. describes a method for manufacturing a known good die array (KGD).
The xe2x80x9cSpin-on Cu Films For ULSI Metallizationxe2x80x9d paper by Hirohiko Murakami, et al., First International Conference on Advanced Materials and Processes for Microelectronics, 1999 describes a spin-on copper (Cu) metal (SOM) process to fill trenches and vias down to 0.3 xcexcm. SOM being a liquid material that contains an organic solvent and dispersed ultrafine particles as source of Cu.
Accordingly, it is an object of the present invention to provide a method of direct wire bonding to a copper metal bonding pad.
A further object of the present invention is to provide a method of achieving a good contact bond between a copper wire and a copper metal bonding pad without using a complicated process.
Another object of the present invention is to provide a method for direct wire bonding to copper bond pads without increasing the contact resistance.
Yet another object of the present invention is to provide a reliable and direct method for direct wire bonding to copper bonding pads.
Other objects will appear hereinafter.
It has now been discovered that the above and other objects of the present invention may be accomplished in the following manner. Specifically, a semiconductor structure having an exposed metal bonding pad within a passivation layer opening is provided. The bonding pad has an upper surface. A bonding element is positioned to contact the bonding pad upper surface. A bonding solution is applied within the passivation layer opening, covering the bonding pad and a portion of the bonding element. The structure is annealed by heating said bonding element to selectively solidify the bonding solution proximate said contact of said bonding element to said bonding pad, bonding the bonding element to the bonding pad.